1. Field of the Invention
The present invention relates to a hand-held percussion power tool with a pneumatic percussion mechanism, such as chisel hammer or hammer drill, and including a percussion piston displaceable in a guide tube and driven by an air spring and that applies blows to an axially displaceable, within certain limits, anvil that, in turn, applies blows to an end surface of a likewise axially movable, within certain limits, working tool.
2. Description of the Prior Art
At unusual operating conditions such as with idle blows applied in a direction of the working tool, with the working tool being lifted off a constructional component, and with reflected, acting in the opposite direction, rebound blows which occur upon striking a relatively rigid reinforcing metal, the percussion mechanism comes out of its optimal normal operational condition and generates strong vibrations which should be damped.
International Publication WO 03/024671 discloses a hand-held power tool having a pneumatic percussion mechanism and a damping member, with the percussion piston having an axially extending outer cone, which is formed by a tapering section, and which frictionally penetrates a steel ring of the damping member and thereby dissipates, at an idle blow, a major part of the displacement energy of the percussion piston over a long axial damping region in the viscoelastic damping member.
German Publication DE 3910398 discloses an arrangement of two anvils in an axially stationary three-part guide sleeve with an elastomeric damping ring. The guide sleeve is provided with two inner radial chamfers at its end sides which are repeatedly impacted by respective outer radial chamfers of an outer radial collar of an anvil at an idle blow, with resulting dissipation of the displacement energy of the percussion piston which is caused by an associated contact friction and the viscoelastic elastomeric damping ring.
According to European Publication EP 1238759, an anvil forms a second, axially spaced, outer radial collar that passes, at an idle blow, an elastomeric damping ring with an inner radial collar, viscoelastically widening the same, whereby additional displacement energy is damped.
According to German Publication De 44 00 779, an anvil is axially displaced in a slide sleeve which is elastically preloaded radially outwardly and frictionally slides in a guide tube. The slide sleeve has, at its opposite end sides, two inner radial chamfers, respectively, associated with respective outer radial chamfers of an outer radial collar formed on the anvil. During an idle blow, the working tool-side inner radial chamfer of the slide sleeve is radially widened, which increases the friction force of the slide sleeve so that, correspondingly, a greater amount of the displacement energy is dissipated. The remaining displacement energy is dissipated by a viscoelastic damping ring that the slide sleeve, together with the anvil, impacts.
The object of the present invention is to provide for robust, long-lasting means for damping idle blows.
Another object of the present invention is a hand-held percussion power tool in which the idle blow path of the anvil and, thereby, a constructional length of the power tool is reduced.